Analysis of Glutamine Deamidation: Products, Pathways, and Kinetics

This manuscript examines glutamine deamidation, which is a spontaneous chemical modification similar to the much more thoroughly characterized asparagine deamidation. Although both processes share similarities and are known to occur in long-lived proteins, here we establish that important differences exist as well. For example, the distribution of isomers generated following glutamine deamidation contains far fewer D-residues. Furthermore, with the exception of QG motifs, glutamine deamidation occurs primarily by direct hydrolysis and produces less isoglutamic acid as a result. In addition, we demonstrate that radical-directed dissociation generates abundant, characteristic, fragment ions that can be used to easily distinguish glutamic acid from isoglutamic acid.